The present invention relates to field effect transistors (FET's), and more specifically, to material removal techniques for forming self-aligned contact openings for field effect transistors.
Semiconductor devices such as FETs, MOSFET's (metal oxide semiconductor FET's), and FinFET's (fin-type FET's) are typically fabricated in sequential processes involving steps materials of different types are deposited or grown, and steps where materials of different types are removed. For example, material is typically removed to form FET contact openings. Various types of material removal processes have been used, such as chemical etching, plasma etching, or reactive ion etching (RIE).
In the past, removal of material for contact openings was dimensionally controlled through conventional masking techniques. With such techniques, a mask could be disposed over portions of the device where material removal was not desired, for example by exposing and curing a soft photoresist mask and removing unexposed areas with solvent or by selectively depositing a hard mask material. A material removal process such as the above-described processes would then be applied through the openings in the mask to remove the underlying material.
More recently, as semiconductor device density has increased, with a concomitant decrease in component sizing and spacing, limitations were reached in the capability of conventional masking techniques to provide accurate registration matching with smaller and more tightly spaced structures beneath the mask. This led to the development of self-aligning technologies such as self-aligned contact (SAC) etching. In a self-aligned contact etch process, adjacent gate structures are provided with an etch-resistant material on the gate sidewall, which prevents etching of the gate itself in the event of mis-alignment of the mask opening edges with the interface between the material removal area and the gate. In the SAC etch process, a material removal technique is used that is selective between the material to be removed and the etch-resistant material on the gate sidewall.